1. About the ONS Longitudinal Study

What is the ONS Longitudinal Study (LS) ?

The LS contains linked census and life events data for a 1% sample of the population of England and Wales. It contains records on over 500,000 people usually resident in England and Wales at each point in time and it is largely representative of the whole population. The LS is the largest longitudinal data resource in England and Wales.

The LS has linked records at each census since the 1971 Census, for people born on one of four selected dates in a calendar year. These four dates were used to update the sample at the 1981, 1991, 2001 and 2011 Censuses. Life events data are also linked for LS members, including births to sample mothers, deaths and cancer registrations. New LS members enter the study through birth and immigration (if they are born on one of the four selected birth dates).

Data on approximately 1 million sample members has been collected over the 40 years of the study. Figure 1 shows LS sample members collected in each census.

The LS documents periods of change over a sample member’s life. Research topics include:

  • health and mortality
  • fertility
  • ageing (age at each census)
  • family formation (including marital status, family and household type)
  • ethnicity and religion
  • migration (country of birth)
  • educational and professional activity
  • social class

The LS has the advantage of a very large sample size and low levels of attrition. This allows for extensive research into subgroups of the population of England and Wales, producing robust results. There are two studies for Scotland and Northern Ireland.

For more detail on the LS, see the publication Longitudinal Study 1971 to 1991 History, organisation and quality of data (available from The National Archives).

What data does the LS contain?

Census data

Census information is collected once every 10 years and mostly relates to people’s circumstances at the time. All information collected on the census forms is included in the LS, for example, age, sex, marital status and many other socio-demographic topics. Census data are also collected on the LS members’ co-residents, as they appear on the same census form. For a full list of data and variables, please access the information within the LS data dictionary (which provides complete information on all variables and tables available to researchers using the LS).

Event data

Event data for LS members usually resident in England and Wales, from the civil registration system, NHS registration systems and the cancer registries, has been added to the LS since Census Day in 1971. This includes:

  • births (entry events)
  • immigration (entry events)
  • deaths (exit events)
  • emigration (exit events)

Other event data includes:

  • live and still births to female LS members
  • deaths of LS members’ spouses
  • deaths of infants born to female LS members
  • cancer registrations
  • re-entries to the LS after an embarkation and enlistment to the armed forces

What happened to LS members over time – cohort interactive tool

Our interactive tool explains what happens to LS members over time. For every new selection please first select beginning date followed by end date. Exits from the LS occur by two means, death or emigration. The quality of death data within the LS is extremely high as death registration is required by law. However, emigration data is not as comprehensive as it relies on LS members informing the NHS when they are leaving the country. It is known that many emigrants do not inform the NHS, causing gaps in the coverage of the data. This largely explains the amount of individuals categorised as lost to follow-up.

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Research and outputs using the LS

CeLSIUS maintains a database of all publications using LS data from the early 1980s onward.

CALLS-Hub has a list of outputs from recent research using the LS, the Scottish LS and the Northern Ireland LS.

Current and completed projects using the LS.

Latest news

For latest news and events see CeLSIUS and CALLS-Hub.

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2. Using the ONS Longitudinal Study

What can the LS be used for?

The LS can be used for several types of analysis, over many different research areas. The studies that make best use of LS data are those that link social, occupational and demographic information to data on life events. Examples include studies of mortality, cancer incidence and survival, and fertility patterns. The individual-level data of the LS means that person-years at risk can be calculated for epidemiological studies.

The ability to combine detailed personal characteristics with area characteristics has proved useful in many studies of health, for example, those looking at environmental effects on health, and those on inequalities in health.

Linked census data for members of the LS allow researchers to examine change between censuses by investigating the same people through two or more censuses.

Studies of social mobility have examined changing class position by age. Information on co-residents of LS sample members has been used to study intergenerational mobility.

The size of the LS makes it suitable for the study of ageing. Studies have used the information collected on the co-residents and family status of LS sample members to examine changes to household and family arrangements that come with age.

Census forms ask about addresses 1 year ago. The linked census data in the LS have been used to study 10-year migration patterns between censuses. In addition, information on place of enumeration in 1939 has been used to study migration over longer periods.

The addition of 2011 Census data on year of arrival (non-UK born residents) and language has meant that individual-level analysis on first- and second-generation migrants and language proficiency is now feasible.

How to use the LS

We actively promote wide use of the LS while maintaining the confidentiality of individuals in its LS sample. To ensure confidentiality, the data can only be accessed in secure settings at our offices in London, Newport (South Wales) and Titchfield (Hampshire). Only statistical analysis or data tabulations are released to researchers through an output clearance process.

Researchers need to make an application to access the LS for research purposes. A user support service is available to help researchers.

This includes:

  • advice on sample sizes and the suitability of the LS for particular projects
  • advice on data content and linkage issues
  • helping you through the application procedure
  • identifying the variables and the study population to be included in an extract
  • making data extracts
  • transforming data and producing the tables or files necessary for your analyses
  • advising on clearance procedures and confidentiality rules

Information and support for UK-based users from the academic, statutory and voluntary sectors can be obtained from the Centre for Longitudinal Study Information and User Support (CeLSIUS) by emailing Celsius@ucl.ac.uk. All other users should contact our Longitudinal Study Development Team (LSDT): LongitudinalStudy@ons.gov.uk.

If you are interested in using the LS, please contact CeLSIUS. A step-by-step guide to using the LS is available from the CeLSIUS website.

LS user resources

The data dictionary is a useful resource for LS users. It gives details of the large number of different variables in the LS.

Census forms

Each census in England and Wales used two types of form: one for private households and another for communal establishments. The form for communal establishments does not contain questions about relationships in a household or questions about household amenities. Copies of the census forms used to collect LS data are available to download from census forms 1971 to 2011.

Census definitions and concepts

The publication Longitudinal Study 1971 to 1991: History, organisation and quality of data (available from the National Archives) is the definitive resource for information about the LS from 1971 to 1991. It provides the best source of information on how events data are linked to the LS and the quality of event information from 1971 to 1991.

Definitions and concepts change at each census. The related documents describe those used at each census, such as "enumerated population", "usual residence", "size of family" or "economic position".

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3. Methodology and quality in the ONS Longitudinal Study

The LS contains linked census and life event information for a 1% sample of the population of England and Wales since 1971.

Data on the extent to which individuals are enumerated, traced and linked correctly at each census are vital for accurate use of the LS. Likewise data on the demographic characteristics of those previously in the LS without a valid exit event and not found at each census, or those individuals with multiple enumerators at the time of the census.

Detailed reports are available to download on the quality of linkages, and success rates in tracing and linking census records to the LS since 1971. In addition, more detailed data on linkage, tracing and sampling by main demographic characteristics are also available to download.

In addition to census data, the LS includes data on a number of registered events occurring to LS members. A detailed report on event quality is available to download.

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4. Find out more

There are several ways you can find out more about the LS.

To discuss a potential research project, please contact the Centre for Longitudinal Study Information and User Support (CeLSIUS). CeLSIUS is an Economic and Social Research Council (ESRC) funded support team for UK academic, government, statutory and voluntary sector users of the LS.

To find out more about the CeLSIUS, please telephone +44 (0)20 7679 1995 or email: celsius@ucl.ac.uk

To find out more about the LS history, data and processes, please contact the LS Development Team by telephone +44 (0)1329 444696 or email: longitudinalstudy@ons.gov.uk

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